Allow developers to create their own user space

It would be wonderful if Microsoft and the windows team documented how developers could create their own userspace. The NT Kernel was designed for this, and it would allow better extensibility of the overall OS. It also would be a way to partial opensource Windows. You could license the kernel at a low price, and let others build the user space.  This would be in the vain of the original WSL, but it would allow any developer skilled enough to bring enhancements to the system.